Fibromyalgia (FM) is a syndrome characterized by chronic widespread pain and the presence of specific tender points. The prevalence of FM has been estimated at 2-7 % of the general global population. The presence of FM in several rheumatic diseases with a structural pathology has been reported as 11-30 %. The objectives of this study were to determine the prevalence of FM and to evaluate the possible relationship between FM existence and disease activity among rheumatic diseases. The study group included 835 patients-197 rheumatoid arthritis (RA), 67 systemic lupus erythematosus (SLE), 119 ankylosing spondylitis (AS), 238 osteoarthritis (OA), 14 familial Mediterranean fever (FMF), 53 Behçet's disease (BD), 71 gout, 25 Sjögren's syndrome (SS), 20 vasculitis, 29 polymyalgia rheumatica (PMR), and two polymyositis (PM)-with or without FM. Recorded information included age, gender, laboratory parameters, presence of fatigue, and disease activity indexes. The prevalence of FM in patients with rheumatologic diseases was found to be 6.6 % for RA, 13.4 % for SLE, 12.6 % for AS, 10.1 % for OA, 5.7 % for BD, 7.1 % for FMF, 12 % for SS, 25 % for vasculitis, 1.4 % for gout, and 6.9 % for PMR. One out of two patients with PM was diagnosed with FM. Some rheumatologic cases (AS, OA) with FM were observed mostly in female patients (p = 0.000). Also, there were significant correlations between disease activity indexes and Fibromyalgia Impact Questionnaire scores for most rheumatologic patients (RA, AS, OA, and BD) (p < 0.05; respectively, r = 0.6, 0.95, 0.887, and 1). Concomitant FM is a common clinical problem in rheumatologic diseases, and its recognition is important for the optimal management of these diseases. Increased pain, physical limitations, and fatigue may be interpreted as increased activity of these diseases, and a common treatment option is the prescription of higher doses of biologic agents or corticosteroids. Considerations of the FM component in the management of rheumatologic diseases increase the likelihood of the success of the treatment. © 2014 Springer-Verlag.